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With the number of smartphone users rapidly rising, we’re seeing more and more websites providing content specifically designed to be browsed on smartphones. Today we are happy to announce that Googlebot-Mobile now crawls with a smartphone user-agent in addition to its previous feature phone user-agents. This is to increase our coverage of smartphone content and to provide a better search experience for smartphone users.
Here are the main user-agent strings that Googlebot-Mobile now uses:

The content crawled by smartphone Googlebot-Mobile will be used primarily to improve the user experience on mobile search. For example, the new crawler may discover content specifically optimized to be browsed on smartphones as well as smartphone-specific redirects.
One new feature we’re also launching that uses these signals is Skip Redirect for Smartphone-Optimized Pages. When we discover a URL in our search results that redirects smartphone users to another URL serving smartphone-optimized content, we change the link target shown in the search results to point directly to the final destination URL. This removes the extra latency the redirect introduces leading to a saving of 0.5-1 seconds on average when visiting landing page for such search results. Update 9 August 2013: If a site uses separate URLs to serve desktop and smartphone users, and if we discover accurate rel-alternate-media annotations linking the desktop and smartphone pages, our algorithms may change the link target shown in the search results to point directly to the smartphone page.
Since all Googlebot-Mobile user-agents identify themselves as a specific kind of mobile, please treat each Googlebot-Mobile request as you would a human user with the same phone user-agent. This, and other guidelines are described in our previous blog post and they still apply, except for those referring to smartphones which we are updating today. If your site has treated Googlebot-Mobile specially based on the fact that it only crawls with feature phone user-agents, we strongly recommend reviewing this policy and serving the appropriate content based on the Googlebot-Mobile’s user-agent, so that both your feature phone and smartphone content will be indexed properly.
If you have more questions, please ask on our Webmaster Help forums.Posted by Yoshikiyo Kato, Software Engineer